Thursday, May 02, 2013

New materials to capture methane

Methane capture in zeolite SBN. Blue represents adsorption sites, which
are optimal for methane (CH4) uptake. Each site is connected to three other
sites (yellow arrow) at optimal interaction distance.

Scientists at Lawrence Livermore National
Laboratory(LLNL) and UC Berkeley and have discovered new
materials to capture methane, the second highest concentration greenhouse gas
emitted into the atmosphere.

Unlike carbon dioxide, the largest emitted
greenhouse gas, which can be captured both physically and chemically in a
variety of solvents and porous solids, methane is completely non-polar and
interacts very weakly with most materials.

"Methane capture poses a challenge that
can only be addressed through extensive material screening and ingenious
molecular-level designs," Maiti said.

Methane is far more potent as a greenhouse gas
than CO2. Researchers have found that the release of as little as 1
percent of methane from the Arctic alone could have a warming effect
approaching that being produced by all of the CO2 that has been pumped into the
atmosphere by human activity since the start of the Industrial Revolution.

Methane is emitted at a wide range of
concentrations from a variety of sources, including natural gas systems,
livestock, landfills, coal mining, manure management, wastewater treatment,
rice cultivation and a few combustion processes

Zeolites are unique structures that can be used for many different types
of gas separations and storage applications because of their diverse topology
from various networks of the framework atoms. In the team's simulations, one
specific zeolite, dubbed SBN, captured enough medium source methane to turn it
to high purity methane, which in turn could be used to generate efficient
electricity.

"We used free-energy profiling and
geometric analysis in these candidate zeolites to understand how the
distribution and connectivity of pore structures and binding sites can lead to
enhanced sorption of methane while being competitive with CO2 sorption at the
same time," Maiti said.

Other zeolites, named ZON and FER, were able to concentrate dilute
methane streams into moderate concentrations that could be used to treat
coal-mine ventilation air.